1. Field of the Invention
This invention relates to improvements in a heat pump type air conditioning system for an automotive vehicle in which a passenger compartment is heated and refrigerated under the action of engine coolant and refrigerant, and more particularly to the improvements to solve various problems encountered in conventional similar heat pump type air conditioning systems so as to offer the heat pump type air conditioning system suitable for practical use.
2. Description of the Prior Art
Hitherto, heat pump type air conditioning systems have been developed for automotive vehicles. Such air conditioning systems carry out both refrigeration and heating for a passenger compartment under cycle operations using a refrigerant. The air conditioning systems include a sub-condenser or interior heat exchanger disposed inside the passenger compartment, in which high temperature and pressure refrigerant from a compressor is introduced into the sub-condenser so as to be used as a heat source for heating the passenger compartment. A main condenser or exterior heat exchanger is disposed outside the passenger compartment. Additionally, a four-way valve is provided to change over flow of the refrigerant from the sub-condenser to the main condenser and vise versa to accomplish a changeover between a refrigeration operation and a heating operation of the air conditioning system. More specifically, the refrigerant discharged from the compressor is introduced to the main condenser during the refrigeration operation, whereas the refrigerant is directly introduced to the sub-condenser through a bypass passage which is formed bypassing the main condenser.
Such heat pump type air conditioning systems have been recently mounted on a part of high quality cars and so-called one box-type cars having a relatively large space, in which they a so-called dual air conditioning type including a front unit for air-conditioning a front region (for example, a front seat part) of the passenger compartment and a rear unit for air-conditioning a rear region (for example, a rear seat part) of the passenger compartment. Accordingly, the front and rear regions of the passenger compartment can be independently air-conditioned so as to achieve a comfortable air conditioning for the passenger compartment. Such air conditioning systems operate as follows: During the heating operation of the air conditioning system, the front unit uses engine coolant as a heat source while the rear unit uses as a heat source a high temperature and pressure refrigerant which is compressed by the compressor. Such air conditioning systems are arranged to pump up heat from the low temperature outside air in the circulating process or refrigeration cycle of the refrigerant and uses it to heat the passenger compartment.
Such air conditioning systems encounter with problems in case of carrying out the heating operation of the passenger compartment of the automotive vehicle. For example, when the temperature of the outside air is low, for example, in the morning in winter, the temperature of the engine coolant is low at the engine starting, and the temperature rise of the refrigerant is not sharp. Consequently, it is difficult to put the air conditioning system into such a state as to blow warm air into the passenger compartment simultaneously with the starting of operation of the air conditioning system, so that the air conditioning system is low in quick or instant heating ability and is low in heating performance. Particularly in the one-box type cars which provided with a diesel engine and are large in space of the passenger compartment, the rate of temperature rise of the engine coolant is low as compared with automotive vehicles provided with a usual gasoline engine while it is required to heat the large space, and therefore there is such a tendency as to be low in quick heating ability and heating performance for the passenger compartment. In view of this, a heat pump type air conditioning system of the following type has now been proposed: The refrigerant is heated under the action of heat of the coolant for a driving system in an electric vehicle thereby to be increased in enthalpy and becoming high in temperature. Accordingly, the thus heated refrigerant exhibits a high heating ability of the air conditioning system. Such a heat pump type air conditioning system is disclosed in Japanese Patent Provisional Publication No. 7-101227.
Thus, the various heat pump type air conditioning systems and improvements therefor have been developed and proposed.
However, the above-discussed heat pump type air conditioning systems have encountered a variety of drawbacks which will be discussed below. That is, it is usual to carry out an on-off control of the compressor by making an on-off control of a magnetic clutch (disposed between the compressor and an engine) in accordance with the discharge pressure of the compressor in order to protect the compressor from its breakage when the discharge pressure of the compressor excessively rises. The discharge pressure of the compressor is detected by a pressure sensor. However, in case of protecting the compressor only under the on-off control of the compressor, shock (impact) and noise are generated with the on-off control (for example, the on-off action of the magnetic clutch) of the compressor. It will be understood that the on-off actions of the magnetic clutch correspond respectively to a connection and a disconnection between the compressor and the engine. These connection and disconnection tend to readily be transmitted as shock to the driver, thereby lowering the drivability of the vehicle.
Further, in order to cause the heat pump type air conditioning systems to exhibit a high heating performance, it is required to recover the refrigerant accumulated in the exterior heat exchanger to the compressor thereby using a large amount of the refrigerant for the heating operation of the air conditioning system. In this regard, the above-discussed air conditioning systems of the dual air conditioning type mounted on the one box-type cars and the like have a relatively large volume condenser and a relatively long piping, so that a considerable time is required to recover the refrigerant. Additionally, for example in case of accomplishing the refrigeration and heating operations of only the rear unit, the refrigerant becomes unnecessary for the front unit. Accordingly, if the refrigerant (for the front unit) accumulated in the evaporator and the like are recovered, a large amount of the liquid state refrigerant is supplied to the compressor, thereby causing the fears of compressing the liquid state refrigerant, and of cleaning the inside of the compressor with the liquid state refrigerant. This degrades the reliability of the compressor itself.